1. Field of The Invention
This invention relates to power control mechanisms for controlling signal strength in a Mobile Wireless Commination System, and in particular to the initial power at which signals to and from mobile end-user devices and a fixed base station should be transmitted.
2. Description of Related Art
In existing systems, a mobile end-user device seeking to initiate communication with a base station broadcasts a request signal at increasing power levels until acknowledged by the base station. Likewise, a base station pages a mobile end-user device at increasing power levels until the end-user device responds. In each situation, one broadcasting station in the communication system ramps the power until a reasonable SNR is achieved by the second receiver. This ramping of power can lead to a signalling exchange procedure which can take sometime, since typically each station is broadcasting over a different channel (particularly in cellular radio telephone systems). It can also lead to interference between mobile end-user devices and to a loss of signal quality of other users of the wireless communication system.
EP 682418 A2 describes a fast, closed loop power control for a mobile radio telecommunication system, which is directed to the steady state operation of closed loop power control. Such a system is common in "second generation" systems, which are circuit switched wireless communication systems. A closed loop functions only if both transceivers in a wireless communication link are already synchronised and exchanging information. The power control algorithm makes use of this established bi-direction link, to exchange information on power levels. The received power is measured and the information fed back to the transmitter, allowing it to adjust its power level to an optimal value.
Future wireless communications systems will support a wide range of services including packet services and, therefore, are likely to be highly dynamic. Thus, the initial set up will be increasingly important, as compared with the steady state, and reasonable power levels must be reached immediately. There is thus a need for power control mechanisms between stations in a mobile wireless communication system which functions at start up and which decreases the time taken to establish an efficient power level.